1. Field of the Invention
The present invention relates to a conveyance system for conveying one or more wafers between a plurality of wafer processing apparatus.
2. Description of the Related Art
The processes for manufacturing IC's and LSI require a lot of processing of wafers. Therefore in the processes for manufacturing IC's and LSI sequentially, wafers are conveyed to the processing apparatus for performing each process. Here, FIG. 1 is a schematic plan view showing an equipment for a lot of processing of wafers. In the drawing, the production equipment sequentially performs processes A-Z on the wafers, and the wafer processing apparatus A, wafer processing apparatus B, . . . , wafer processing apparatus Z are arranged as shown. These wafer processing apparatus are provided with stockers SA, SB, . . . , SZ for each processing apparatus. Each stocker houses a plurality of cassettes capable of accommodating 10-20 stacked wafers. Additionally, n (n is a natural number) wafer processing apparatus A1-An are arranged in a row. And n (n is a natural number) wafer processing apparatus B, . . . , Z are arranged in the same as the n wafer processing apparatus A1-An. And in the drawing, the wafer processing apparatus are numbered from 1 to n. A rail AR, BR, . . . , ZR from the stocker corresponding to each wafer processing apparatus are provided parallel to the n aligned wafer processing apparatus. The rail AR, BR, . . . , ZR are arranged for guiding an in-process cassette transfer apparatus which is not shown, and for performing in-process cassette conveyance.
With this structure, a cassette transfer apparatus traveling along the rail AR withdraws a cassette from the stocker SA, moves over the rail AR, and places the cassette in front of the wafer processing apparatus A1. Then, when this type of cassette transfer operation has been performed with respect to n wafer processing apparatus A and the cassette transfer operation has ended, as shown in FIG. 2, a cassette 4 housing a plurality of stacked wafers is positioned in front of n wafer processing apparatus A. A wafer transfer apparatus 2 is arranged between the cassette 4 and the wafer processing apparatus A. The wafer transfer apparatus 2 takes out a wafer in the cassette 4 and sets it in the wafer processing apparatus A. Then, after the set wafer has undergone the process A by the wafer processing apparatus A, the A-processed wafer is extracted from the wafer processing apparatus A by means of the wafer transfer apparatus 2, and rehoused inside the cassette 4. When this type of process has been performed with respect to every wafer in cassette 4, they are returned to the stocker SA by means of the in-process cassette transfer apparatus which travels along the rail AR shown in FIG. 1. The in-process cassette transfer apparatus performs the action of returning the cassette 4 containing the A-processed wafers to the stocker SA with respect to n wafer processing apparatus A1-An.
The cassette 4 in which wafers which have undergone the process A has been housed is moved from the stocker SA to the stocker SB provided in correspondence to the wafer processing apparatus B. Here, the movement of the cassette 4 between stockers is performed by means of an inter-process cassette transfer apparatus not shown. The inter-process cassette transfer apparatus is provided movably on the rail SR provided parallel to each stocker in the left-right direction in the drawing. This inter-process cassette transfer apparatus withdraws the cassette 4 from the stocker corresponding to the wafer processing apparatus of the previous stage, moves to the position in front of a stocker corresponding to the wafer processing apparatus of the next step, and houses the cassette 4 in this stocker. In this way, the cassette 4 is moved between stockers.
When the cassette 4 is moved from the stocker SA to the stocker SB by the inter-process cassette transfer apparatus as described above, the cassette 4 is sequentially conveyed from the stocker SB in front of the n wafer processing apparatus B by means of the in-process cassette transfer apparatus which travels along the rail BR. Then, the wafer transfer apparatus provided for each wafer processing apparatus B takes out one wafer at a time from the cassette 4 as in the case of the process A described above, sets it in the wafer processing apparatus B, to perform the process B by means of the wafer processing apparatus B. Then, the B-processed wafers are once again returned to the cassette 4, and when all of the B-processed wafers have been accommodated into the cassette 4, the cassette 4 is returned from in front of the n wafer processing apparatus B to the stocker SB by means of the in-process cassette transfer apparatus. LSI and IC's are produced by repeating this type of operation until the process Z.
However, in the semiconductor producing equipment described above, it is not possible to go on to process B until process A has been completed with respect to all of the wafers housed in the cassette 4 housed in the stocker, thus requiring a large amount of time to produce semiconductors which necessitate a large number of processing steps. Additionally, during the period from when the process A has been performed until the next process B is performed, the processed wafers are left for a long time inside the cassette 4. For example, if the wafers are left for a long time after performing a wafer cleansing process before going on to the next coating process, dust may adhere to the wafers or the wafers may oxidize, thus reducing the yield.
Additionally, with the above-described production equipment, although the production time is not a problem when performing mass production of the same type of product, in the case of small-scale production of prototype or different types of products, then the same amount of production time is required as with mass production even though the number produced is small. That is, a large amount of time is required to produce prototype or small-scale production products. Additionally, since a large number of transfer apparatus such as in-process cassette transfer apparatus, inter-process cassette transfer apparatus and wafer transfer apparatus are required, the cost of equipment production becomes large, thereby increasing the production cost of the final product.